This invention relates to medico-surgical devices.
The invention is more particularly concerned with medico-surgical catheters or probes having electrodes.
Conventionally, medico-surgical catheters provided with an electrode have a metal wire extending along the catheter which is insulated along its length such as by the material of the catheter along which it extends. The electrode may be formed by a separate metal member welded or soldered to the wire and is located on the surface of the catheter where it is exposed for contact with adjacent tissue. Examples of such devices are described in EP 0366127, U.S. Pat. No. 3,951,136, EP 0334086 and WO 92/17150.
There are several problems with using metal electrodes. Many metals suitable for use as electrodes are not very biocompatible. Although in some circumstances they can be used satisfactorily, where the electrode has to have a large surface area or is inserted in the body for prolonged periods, it can lead to adverse reactions. Inert metals which are biocompatible, such as gold or platinum, are expensive and, therefore, only suitable for use on reusable catheters. Because of the risk of cross infection, it is preferable in most circumstances to use disposable, single-use catheters which must be of low cost. Also, it is often desired for the main body of the catheter to be of a plastics material because of its flexibility and softness but these plastics materials are often unsuitable for the repeated sterilization required in reusable catheters.
Another problem with using metal electrodes on a plastic catheter, probe or similar body is the difficulty of providing a secure mount. The difference between the physical properties of metal and plastics increases the risk that the electrode will separate from the body on flexing or other deformation. In medical applications, it is clearly very important that there is no risk of the electrode coming away from the catheter or of damaging the catheter itself in such a way that a part of the catheter becomes detached. Furthermore, it can be difficult to assembly a metal electrode into a plastics body without damaging the plastics body. Where it is desired to produce a flexible catheter or probe with an electrode, the hard, rigid nature of metal materials can compromise the overall flexibility of the catheter.